The present invention relates to a mask protective device for preventing sticking of dust and other particles on a mask or a reticle (hereinafter, referred to as the "mask") which is used for photolithography in manufacturing processes of an integrated circuit.
The term "mask" means an original plate used for transferring a designed layout pattern onto a semiconductor wafer in the process of photolithography.
If dust or other particles stick on the mask in the process of photolithography, the dust or particles are also projected onto the semiconductor wafer. This may be a cause of producing defectives. In order to solve this problem and prevent sticking of dust and other particles on the mask, a mask protective device is used.
The mask protective device comprises a frame, the size of which is set to surround the layout pattern of the mask, and a transparent thin film closing one opening end face of the frame. The mask protective device is mounted to the mask by bonding the other opening end face of the frame to the mask with bonding means such as an adhesive tape. The mask is then covered by the thin film disposed apart from the mask, thereby protecting the mask from dust and other particles.
As the mask protective device is bonded on the mask as mentioned above, however, the airtightness in the device is quite high so that the thin film sometimes swells or dents due to change in atmospheric pressure or in temperature. The swell or dent in the thin film may change the optical characteristics of the thin film and/or, in case of severely swelling or denting, damage the thin film by that the thin film comes in contact with the mask or a lid of a casing which accommodates the mask and the mask protective device therein.
In order to solve the aforementioned problem, Utility Model Publication No. S63(1988)-39703 (U.S. Pat. No. 4,833,051) discloses a mask protective device which has a frame provided with at least one vent which is closed by a filter to prevent trespassing of dust or other particles. According to this mask protective device, the mask protective device has gas permeability even when it is mounted to the mask, thereby avoiding the swell and dent in the thin film due to the change in atmospheric pressure or in temperature.
However, in the mask protective device of the aforementioned Utility Model, since the filter is bonded directly on the outer surface of the frame to close the vent, its quantity of gas flow is relatively small and its adaptability to the changes in atmospheric pressure and in temperature is not so well.